For what it's worth, my slim pocket volume "The Marling Menu-Master for Italy" defines "scampi" as follows:
SCAMPI: Actually a large prawn, best of which comes from the Adriatic, but again, there is confusion, for a salt-water crayfish can be called a Scampi, and what is a Gambero in one place will be called a Scampi in another."
I certainly don't claim to be an expert on this, but (leaving aside their treating the word "scampi" as a singular) I had assumed they were correct. Are they not?